EPAC: ALETTA - Post-Tropical

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Re: EPAC: ALETTA - Hurricane

#181 Postby cycloneye » Sat Jun 09, 2018 10:26 am

Ntxw wrote:Looks to be winding down. She should pick up a point here and there for ACE which will end up ~10 units or about so.

http://i66.tinypic.com/358bcw4.gif


As of 0900z,it had 9.6 ACE units.
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Re: EPAC: ALETTA - Hurricane

#182 Postby USTropics » Sat Jun 09, 2018 1:24 pm

the 40+ knots of shear at the 350-800hp levels looks to have finally decoupled the system. LLC is visible on the SW quadrant now:

Image
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Re: EPAC: ALETTA - Hurricane

#183 Postby storminabox » Sat Jun 09, 2018 1:32 pm

USTropics wrote:the 40+ knots of shear at the 350-800hp levels looks to have finally decoupled the system. LLC is visible on the SW quadrant now:

Image


What a dramatic change from 24 hours ago! Looks to be completely falling apart. I bet this thing will weaken a lot quicker than what the Nhc is saying.
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Re: EPAC: ALETTA - Hurricane

#184 Postby Sciencerocks » Sat Jun 09, 2018 2:39 pm

Easy come, easy go! Amazing how once cyclones hit lower sst's(stable air) they also lose control of their anti-cyclones and get ripped apart by what aided them before. lol
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Re: EPAC: ALETTA - Hurricane

#185 Postby NDG » Sat Jun 09, 2018 2:58 pm

Sciencerocks wrote:Easy come, easy go! Amazing how once cyclones hit lower sst's(stable air) they also lose control of their anti-cyclones and get ripped apart by what aided them before. lol


Not only cooler SSTs & drier air but also mid level shear which kills tropical systems even faster, as seen on satellite loop.
One thing that I was right on is that Aletta was not going to be a long tracker.

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Re: EPAC: ALETTA - Hurricane

#186 Postby cycloneye » Sat Jun 09, 2018 3:33 pm

Hurricane Aletta Discussion Number 17
NWS National Hurricane Center Miami FL EP022018
300 PM MDT Sat Jun 09 2018

Aletta has rapidly weakened during the past several hours, with the
main convection currently dissipating to the north and northeast of
the now-exposed low-level center. The initial intensity is reduced
to a possibly generous 65 kt based on a combination of subjective
and objective satellite intensity estimates. Rapid weakening should
continue due to a combination of shear, decreasing sea surface
temperatures along the forecast track, and entrainment of dry air.
Based on current trends, the new intensity forecast shows a faster
demise for Aletta than the previous advisory, with the system now
forecast to weaken to a depression by 36 h, and degenerate to a
remnant low by 48 h.

The initial motion is quite uncertain due to Aletta being south of
where the earlier microwave fixes indicated it to be and due to the
exposed center moving southwestward. This advisory will use a
longer-term motion of 275/5. Most of the track guidance forecasts
the cyclone to resume a west-northwestward motion over the next few
hours, then again turn westward by 24-36 h. After that time the
remnants of Aletta are expected to move slowly west-southwestward.
The new forecast track follows this basic scenario, but it lies well
to the south of the center of the guidance envelope and the
consensus models based on the current trends. An alternate scenario
is that Aletta never makes the west-northwestward turn, which would
result in the decaying system tracking south of the new forecast
track.


FORECAST POSITIONS AND MAX WINDS

INIT 09/2100Z 16.1N 113.9W 65 KT 75 MPH
12H 10/0600Z 16.6N 114.7W 50 KT 60 MPH
24H 10/1800Z 17.0N 115.7W 35 KT 40 MPH
36H 11/0600Z 17.1N 117.0W 25 KT 30 MPH
48H 11/1800Z 16.9N 118.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 12/1800Z 16.6N 120.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 13/1800Z 16.0N 121.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 14/1800Z 15.5N 122.5W 15 KT 15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven
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Re: EPAC: ALETTA - Hurricane

#187 Postby Kazmit » Sat Jun 09, 2018 3:51 pm

Crazy how fast this went up and came back down again.
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Re: EPAC: ALETTA - Hurricane

#188 Postby Kingarabian » Sat Jun 09, 2018 4:01 pm

Kazmit wrote:Crazy how fast this went up and came back down again.


Pretty crazy how In 48 hours, Aletta went from TS->MH->TS.
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Re: EPAC: ALETTA - Tropical Storm

#189 Postby cycloneye » Sat Jun 09, 2018 9:36 pm

Tropical Storm Aletta Discussion Number 18
NWS National Hurricane Center Miami FL EP022018
900 PM MDT Sat Jun 09 2018

Aletta's downfall has been remarkable. All associated deep
convection has dissipated due to 25 kt of southerly shear and
marginally warm sea surface temperatures, leaving a swirl of low-
to mid-level clouds. Dvorak estimates are falling as fast as they
can based on rules, and the advisory intensity is being set at 50
kt. The latest SATCON numbers support this estimate.

Aletta has been losing latitude through the day, moving
west-southwestward since this morning. Recent satellite images
seem to suggest that the cyclone is now moving westward, and the
motion estimate is 270/6 kt. The dynamical and simpler Trajectory
and Beta Models (TAB) have been insisting that Aletta will turn
generally northwestward, but that obviously hasn't happened. The
models seem to be assuming that Aletta is still producing
convection, with the deeper modeled vortex being steered toward the
northwest. With no deep convection, the shallow circulation is
likely to continue generally westward or south of due west, and the
NHC forecast is along the southern edge of the guidance, roughly
between the ECMWF model and the skill-baseline Trajectory-CLIPER
(TCLP) model.

The new NHC intensity forecast now makes Aletta a remnant low in 36
hours, but if deep convection doesn't redevelop, that transition
will occur on Sunday. Fast weakening is expected to continue, and
the official forecast closely follows the HCCA model and the
intensity consensus during the first 24-36 hours. After that, the
remnant low's winds are based on the GFS and ECMWF forecast wind
fields.

FORECAST POSITIONS AND MAX WINDS

INIT 10/0300Z 15.9N 114.3W 50 KT 60 MPH
12H 10/1200Z 15.9N 115.2W 35 KT 40 MPH
24H 11/0000Z 15.9N 116.4W 30 KT 35 MPH
36H 11/1200Z 15.8N 117.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 12/0000Z 15.8N 118.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 13/0000Z 15.8N 120.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 14/0000Z 15.5N 121.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 15/0000Z 15.0N 121.5W 15 KT 15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg
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Re: EPAC: ALETTA - Tropical Storm

#190 Postby cycloneye » Sun Jun 10, 2018 4:58 am

Tropical Storm Aletta Discussion Number 19
NWS National Hurricane Center Miami FL EP022018
300 AM MDT Sun Jun 10 2018

After being devoid of thunderstorms for some time, a burst of
deep convection developed over the northern semicircle of Aletta.
This has probably made the weakening of the cyclone a little less
rapid than had been occurring over the last day or so. The current
intensity estimate is down to 45 kt based on a blend of subjective
Dvorak estimates from TAFB and SAB along with objective Dvorak
estimates from UW-CIMSS. In spite of the recent increase of
thunderstorm activity, which is thought to be temporary, strong
shear and marginal SSTs are likely to cause continued weakening and
Aletta is expected to degenerate into a remnant low in a day or so.
This is consistent with the intensity model consensus.

The system continues to move slowly westward, or around 280/5 kt.
A weak low- to mid-level ridge to the north of Aletta should
maintain this general motion for a few days. Later in the period,
steering currents are forecast to become very weak, and little
motion is indicated at days 4 and 5. By that time, however,
Aletta should be a very weak post-tropical cyclone. The official
forecast is similar to the previous one and on the southern side of
the track model guidance suite.

FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 16.0N 114.5W 45 KT 50 MPH
12H 10/1800Z 16.1N 115.5W 35 KT 40 MPH
24H 11/0600Z 16.1N 116.8W 30 KT 35 MPH
36H 11/1800Z 16.0N 117.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 12/0600Z 15.9N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 13/0600Z 15.8N 120.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 14/0600Z 15.6N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 15/0600Z 15.4N 121.2W 15 KT 15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Pasch
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Re: EPAC: ALETTA - Tropical Storm

#191 Postby Ntxw » Sun Jun 10, 2018 8:51 am

Aletta hasn't entirely given up yet. Her W/SW movement is paralelling the higher shear instead of taking it head on. Probably not much but resilient system.

Image
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Re: EPAC: ALETTA - Tropical Storm

#192 Postby cycloneye » Sun Jun 10, 2018 9:37 am

Tropical Storm Aletta Discussion Number 20
NWS National Hurricane Center Miami FL EP022018
800 AM PDT Sun Jun 10 2018

Shortly after 0600Z, a strong burst of deep convection, containing
very cold cloud top temperatures of -90C and significant lightning
activity, developed northwest of the previously exposed low-level
circulation center. The center has since made a jog toward the
northwest closer to the strongest convection. The initial intensity
has been decreased to 40 kt, based on average of TAFB current
intensity (CI) and the current T-number estimates. Although the
general trend for the next 24 h or so should be a gradual erosion of
the deep convection due to the entrainment of drier and more stable
air and the cyclone moving over SSTs less than 26C. However, there
will likely be intermittent bursts of convection that will slow the
weakening rate and maintain Aletta as a tropical cyclone. By 36 h
and beyond, increasing southwesterly vertical wind shear of 15-20
kt, coupled with the aforementioned stabilizing environment, should
cause all convection to dissipate, resulting in Aletta becoming a
shallow remnant low pressure system. The new NHC intensity forecast
is similar to the previous advisory, and closely follows the HCCA
and IVCN consensus intensity models.

Despite the recent northwestward jog, the average motion over the
last 36 h yields a motion of 280/05 kt, similar to the previous
advisory motion. Aletta is forecast by most of the model guidance
to move westward to west-northwestward, or around 280/05 kt for the
next 24 h or so. After that, a weak low- to mid-level ridge to the
north of the cyclone is expected to build southward slightly,
forcing the weak and shallow cyclone toward the west-southwest. By
days 4 and 5, the system could stall as it comes under the
increasing influence of strengthening Tropical Storm Bud, currently
located about 700 nmi to the east-southeast. The official forecast
track is similar to the previous advisory and is in the middle of
the track model guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 16.5N 115.1W 40 KT 45 MPH
12H 11/0000Z 16.6N 116.0W 35 KT 40 MPH
24H 11/1200Z 16.7N 117.2W 30 KT 35 MPH
36H 12/0000Z 16.6N 118.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 12/1200Z 16.4N 119.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 13/1200Z 16.2N 120.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 14/1200Z 16.0N 120.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 15/1200Z 15.8N 121.0W 15 KT 15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart
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Re: EPAC: ALETTA - Tropical Storm

#193 Postby cycloneye » Sun Jun 10, 2018 3:34 pm

Tropical Storm Aletta Discussion Number 21
NWS National Hurricane Center Miami FL EP022018
200 PM PDT Sun Jun 10 2018

Despite southerly vertical wind shear of about 15 kt, Aletta has
been able to maintain a small cluster of strong convection in the
northwestern quadrant. Recent ASCAT passes missed the now partially
exposed low-level center and much of the inner-core wind field, but
they did manage to capture tropical-storm-force winds in the eastern
semicircle. Also, a Mexican Navy automated weather station on
Clarion Island reported a sustained wind of 33 kt and a gust to 47
kt a few hours ago as an outer band passed over the island. Based on
that observation, along with a TAFB Dvorak estimate of T3.0/45 kt,
the intensity is being maintained at 40 kt for this advisory.

Microwave satellite position fixes indicate a motion of about 280/06
kt since the previous advisory. No significant changes to the
previous forecast track were required. The new model guidance
remains in fair agreement on Aletta moving slowly westward for the
next 48-72 h along the southern periphery of a weak low- to
mid-level ridge to the north of the cyclone. After that time,
steering currents are forecast to collapse, along with Aletta coming
under the influence of rapidly strengthening Hurricane Bud currently
located to the east-southeast, which could result in the shallow
cyclone stalling. The official forecast track is similar to the
previous advisory and remains in the middle of the tightly packed
track model guidance.

Although the wind shear is forecast to weaken to less than 10 kt
during the next 24-36 hours, which would generally favor
re-strengthening, Aletta will also be moving over sub-26C SSTs and
into a drier and more stable airmass. The poor thermodynamics, along
with cold-air stratocumulus clouds already being ingested into the
western and southern quadrants of the cyclone, argues for gradual
weakening to occur over the next day or so, with Aletta degenerating
into a remnant low pressure system by Tuesday. A steady spin down of
the low is expected during the 72-120 hour period, with the shallow
cyclone possibly even dissipating on day 5. The official intensity
forecast is similar to the previous advisory, and closely follows
a blend of the HCCA and IVCN consensus intensity models.

FORECAST POSITIONS AND MAX WINDS

INIT 10/2100Z 16.6N 115.7W 40 KT 45 MPH
12H 11/0600Z 16.6N 116.6W 35 KT 40 MPH
24H 11/1800Z 16.6N 117.6W 30 KT 35 MPH
36H 12/0600Z 16.5N 118.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 12/1800Z 16.4N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 13/1800Z 16.2N 120.6W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 14/1800Z 16.1N 120.9W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 15/1800Z 15.9N 121.1W 15 KT 15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart
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Re: EPAC: ALETTA - Tropical Storm

#194 Postby cycloneye » Sun Jun 10, 2018 9:34 pm

Tropical Storm Aletta Discussion Number 22
NWS National Hurricane Center Miami FL EP022018
800 PM PDT Sun Jun 10 2018

Aletta is maintaining its sheared structure. Although cloud tops
have warmed over the past few hours, the tropical storm is still
producing persistent convection in the northwestern quadrant. Dvorak
classifications from TAFB and SAB have not changed since 6 hours
ago, so the intensity has been held at 40 kt. No change has been
made to the intensity forecast. Aletta has been moving along a
tongue of moderately warm water, which may have allowed convection
to persist up to this point, but the cyclone will soon cross a sharp
SST gradient and enter into a much more stable environment. Once
that occurs, the cyclone will likely lose all convection and become
a remnant low, gradually spinning down over the course of a few
days. While not explicitly shown in this forecast, it is possible
that Aletta will dissipate by the middle to end of the week.

The tropical storm has been moving toward the west-northwest, or
285/6 kt, this evening, but a westward motion is expected to resume
overnight. All of the dynamical models continue to indicate that
Aletta will be steered slowly westward by a mid-level ridge to the
north for the next 24 to 36 hours. After that time, a turn toward
the west-southwest will likely occur as the low-level tradewinds
become the dominant steering feature. From day 3 onward, the
cyclone is expected to become trapped in light low-level flow
between a high pressure system to the northwest and Hurricane Bud to
the east, so the NHC forecast shows little to no movement. The
official track forecast has been adjusted slightly northward for the
first 36 hours due to Aletta's recent short-term west-northwestward
motion, but is not significantly changed from the previous advisory
and remains close to TVCN and HCCA.


FORECAST POSITIONS AND MAX WINDS

INIT 11/0300Z 16.8N 116.2W 40 KT 45 MPH
12H 11/1200Z 16.9N 117.2W 35 KT 40 MPH
24H 12/0000Z 16.9N 118.3W 30 KT 35 MPH
36H 12/1200Z 16.7N 119.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 13/0000Z 16.4N 119.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 14/0000Z 16.2N 120.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 15/0000Z 16.0N 120.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 16/0000Z 16.0N 120.5W 15 KT 15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky
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Re: EPAC: ALETTA - Tropical Storm

#195 Postby cycloneye » Mon Jun 11, 2018 4:44 am

Tropical Storm Aletta Discussion Number 23
NWS National Hurricane Center Miami FL EP022018
200 AM PDT Mon Jun 11 2018

Deep convection associated with Aletta has waned overnight, and as a
result, objective and subjective Dvorak T-numbers have decreased. A
recent ASCAT overpass that was very helpful in locating the center
of Aletta indicated that the cyclone's winds have decreased to
around 35 kt. The tropical storm is forecast to weaken while it
moves over decreasing sea surface temperatures and into a more
stable air mass during the next day or so. Aletta is expected to
degenerate into a remnant low in about 24 hours, but this could
occur sooner if organized deep convection does not redevelop soon.

Recent satellite fixes indicate that the tropical storm is moving
west-northwestward at about 5 kt. The cyclone should turn westward
today, then west-southwestward by Tuesday as it is steered by the
low-level tradewind flow. The low-level flow is expected to become
quite light as Hurricane Bud moves northwestward off the coast of
southwestern Mexico. This should cause Aletta's remnants to become
nearly stationary by mid-week. The track guidance is in fairly
good agreement through 48 hours, but diverges considerably after
that time due to the lack of well-defined steering currents. The
NHC forecast has been shifted slightly eastward at 48 h and beyond
to be closer to the various consensus tracks.

FORECAST POSITIONS AND MAX WINDS

INIT 11/0900Z 17.0N 116.7W 35 KT 40 MPH
12H 11/1800Z 17.0N 117.7W 30 KT 35 MPH
24H 12/0600Z 16.9N 118.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 12/1800Z 16.6N 119.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 13/0600Z 16.3N 119.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 14/0600Z 16.3N 119.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 15/0600Z 16.3N 119.8W 15 KT 15 MPH...POST-TROP/REMNT LOW
120H 16/0600Z...DISSIPATED

$$
Forecaster Brown
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Re: EPAC: ALETTA - Tropical Depression

#196 Postby cycloneye » Mon Jun 11, 2018 9:38 am

Tropical Depression Aletta Discussion Number 24
NWS National Hurricane Center Miami FL EP022018
800 AM PDT Mon Jun 11 2018

Aletta has been devoid of any significant convection for about 8
hours due to the cyclone ingesting dry mid- and upper-level air
along with an abundance of stable, low-level cold-air stratocumulus
clouds. The combination of these unfavorable thermodynamic
conditions and SSTs less than 26C beneath the cyclone should result
in Aletta degenerating into a remnant low pressure system later
today, possibly as early as the next advisory cycle. The initial
intensity of 30 kt is based on an average of Dvorak T- and CI-
numbers from TAFB, and an assumed spin down from the 35-kt winds
noted in 0532 UTC ASCAT data.

Microwave satellite fixes indicate that Aletta has been moving
westward at about 10 kt since the previous advisory. However, this
is likely just a temporary motion due to the decoupling of the
low- and upper-level circulations owing to the loss of convection.
As a result, the advisory motion is estimated to be a slower 270/06
kt. Aletta is expected to move westward today, followed by a turn
toward the west-southwest by Tuesday due to the shallow cyclone
being steered by the low-level easterly to northeasterly tradewind
flow. By days 3 and 4, the steering flow is forecast to weaken
significantly, causing Aletta to possibly stall, due to the remnant
low coming under the influence of major Hurricane Bud's expanding
circulation. The NHC track guidance is in good agreement on this
developing track scenario, and the new forecast track is similar to
the previous advisory and the consensus models HCCA and TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 11/1500Z 16.8N 117.8W 30 KT 35 MPH
12H 12/0000Z 16.7N 118.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 12/1200Z 16.5N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 13/0000Z 16.3N 120.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 13/1200Z 16.1N 120.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 14/1200Z 16.0N 120.2W 15 KT 15 MPH...POST-TROP/REMNT LOW
96H 15/1200Z 16.0N 120.0W 15 KT 15 MPH...POST-TROP/REMNT LOW
120H 16/1200Z...DISSIPATED

$$
Forecaster Stewart
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Re: EPAC: ALETTA - Post-Tropical

#197 Postby cycloneye » Mon Jun 11, 2018 3:36 pm

Post-Tropical Cyclone Aletta Discussion Number 25
NWS National Hurricane Center Miami FL EP022018
200 PM PDT Mon Jun 11 2018

The depression has degenerated into a remnant low pressure system
due to the lack of any convection during the past 14 hours, and is
mainly a large swirl of cold-air stratocumulus clouds now. The
initial intensity of 30 kt is based on a few 29- to 30-kt wind
vectors noted in recent 1703Z and 1803Z ASCAT overpasses. Further
weakening and gradual spin down of the wind field is expected while
the cyclone moves slowly west-southwestward over sub-26 deg C waters
during the next several days, with dissipation forecast to occur by
day 5, if not sooner.

This is the last advisory on this system issued by the National
Hurricane Center. For additional information on the remnant low
please see High Seas Forecasts issued by the National Weather
Service...under AWIPS header NFDHSFEPI and WMO header FZPN02 KWBC.

FORECAST POSITIONS AND MAX WINDS

INIT 11/2100Z 16.6N 118.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
12H 12/0600Z 16.4N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
24H 12/1800Z 16.3N 119.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 13/0600Z 16.1N 120.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 13/1800Z 15.9N 120.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 14/1800Z 15.9N 120.0W 15 KT 15 MPH...POST-TROP/REMNT LOW
96H 15/1800Z 15.9N 119.9W 15 KT 15 MPH...POST-TROP/REMNT LOW
120H 16/1800Z...DISSIPATED

$$
Forecaster Stewart
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gatorcane
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Re: EPAC: ALETTA - Post-Tropical

#198 Postby gatorcane » Mon Jun 11, 2018 3:52 pm

as quickly as Aletta spun up, it spun down just as quick...she was a nice storm to watch and certainly outperformed.
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